1. Field of the Invention
The invention relates to a driving force distribution device for controlling distribution of a driving force to front and rear wheels or to right and left wheels of a vehicle.
2. Description of the Related Art
For example, JP-A-2007-176329 discloses a driving force distribution device for a four-wheel-drive vehicle in which a shift of a sub transmission and a clutch pressing force of a friction clutch are controlled by a single actuator.
The driving force distribution device disclosed in JP-A-2007-176329 is provided with a sub transmission for switching a rotational driving force from an output shaft between two levels, a high speed and a low speed, and transmitting the rotational driving force to a primary output shaft, a friction clutch for transmitting the rotational driving force of the primary output shaft to a secondary output shaft and a ball cam plate for changing a clutch pressing force of the friction clutch in accordance with rotary drive of an actuator.
The driving force distribution device is provided with a rotary drive member coaxially fixed to an output shaft of the actuator. A shifting cylindrical cam for moving a shift fork connected to the sub transmission and a pinion gear engaged with a drive gear of the ball cam plate are respectively arranged on both axial sides of the rotary drive member so as to be relatively rotatable.
Clockwise rotation of the rotary drive member caused by the actuator is transmitted to the pinion gear, and the clutch pressing force of the friction clutch generated by the ball cam plate via the drive gear is changed in response to the rotation of the pinion gear. Rotary motion of the shifting cylindrical cam generated by counterclockwise rotation of the rotary drive member is converted into linear motion by the shift fork, thereby shifting the sub transmission.
A sliding ratchet attached to the rotary drive member so as to be movable in a rotation axis direction is provided so as to be freely coming in and out of a ratchet groove which is formed on an end face of the shifting cylindrical cam. When the ratchet is fitted to the ratchet groove, counterclockwise rotary drive of the rotary drive member is transmitted to the shifting cylindrical cam and the sub transmission is alternately and repeatedly switched between high and low speeds by the shift fork in every reciprocating rotation of the shifting cylindrical cam.